Manufacture of electrical contacts



p 28, 1955 R. E. c. TALBOT ETAL 3,208,129

MANUFACTURE OF ELECTRICAL CONTACTS Filed Nov. 1, 1961 FlG.4.

United States Patent 3,208,129 MANUFACTURE OF ELECTRICAL CONTACTS Ralph Ernest Claude Talbot, London, and Robert Hastings Gray, Kenton, Middlesex, England, assignors to Engelhard Industries Limited, London, England, a British company Filed Nov. 1, 1961, Ser. No. 149,257 Claims priority, application Great Britain, Nov. 3, 1960, 37,865/60 2 Claims. (Cl. 29-155.55)

This invention relates to the manufacture of an electrical contact having one face made from a contact metal selected for its electrical performance, the face being backed by a metal of different composition. Such a bimetallic contact is in many cases desirable in order to economise in the use of an expensive contact metal by employing a backing of a cheaper metal. In other cases, it is desired to select a backing metal which is more readily soldered or welded to a support than is the contact metal itself. The contact metal is usually a noble or precious metal, or an alloy thereof, since such metals are better able to resist deterioration, for example by corrosion or electrical erosion, than are most base metals and alloys.

Whilst bimetallic contacts may take many forms, and may be attached to a suitable support in many ways, a common arrangement is one in which the contact is formed in the shape of a rivet and is attached to the support by a process involving mechanical deformation of part of the contact itself.

Bimetallic contact rivets have been manufactured by processes in which a base metal rivet is first formed, whereafter a noble or precious metal contact surface is then provided by applying a suitable shaped noble or precious metal portion, for example by brazing, welding or soldering. These processes have proved to be costly, and moreover the joining operation usually causes softening of the contact surface, which is undesirable in many applications.

It has been proposed to produce such contacts by first making a copper, or other base metal, plate or sheet with a silver, or other noble or precious metal, surface layer intimately bonded to it. Circular discs are then punched fom this double metal sheet and deformed to the required rivet-like shape with the aid of a press. This method overcomes some of the difficulties encountered in other methods. It can, however, be generally stated that methods of manufacture which rely upon punching from a sheet, result in the production of much scrap, since the sheet cannot be wholly used.

In our British patent specification No. 815,136, a method is described in which a wire of rectangular crosssection is cut into short lengths which are delivered to a contact forming machine and deformed to a rivet-like shape. The wire comprises a noble or precious metal layer intimately bonded to a base metal portion, the layer and portion extending along the length of the wire. During the deforming process in which the material, originally of rectangular cross-section, is converted into the substantially circular cross-section of the final product, it is diflicult to maintain a uniform and closely controlled layer of the precious metal on the base metal.

According to the present invention, there is provided a method of manufacturing a bimetallic electrical contact, wherein a composite slug is prepared by joining wire of noble metal, or an alloy thereof, in end-to-end abutting relationship with a Wire of base metal, or an alloy thereof, and cutting off a length of wire including the abutting joint, said composite slug being thereafter deformed to produce an electrical contact having a contact face of noble metal or alloy thereof.

3,208,129 Patented Sept. 28, 1965 In order that the invention may be more clearly understood and readily carried into effect, an example thereof will now be described with reference to the accompanying drawing, in which:

FIGURE 1 is a diagram illustrating a first stage in the method,

FIGURES 2 and 3 are diagrams illustrating two further stages in the method, and

FIGURE 4 shows an electrical contact rivet manufactured by the method.

Referring now to FIGURE 1, pure copper wire 1 and pure silver wire 2, each of circular cross-section and having a diameter of 0.150, are straightened by conventional means. An end 1A of the copper wire 1 and an end 2A of the silver Wire 2 are prepared by forming plane surfaces at right-angles to the axes of the wires 1 and 2, respectively, and the ends 1A and 2A are brought together at 3, as shown in FIGURE 2. The ends 1A and 2A are then electric-resistance butt-welded together at 3 in such a way, e.g., pressure-wise that no upset or swelling occurs at the welded joint. A portion of the wire, including the welded joint, is then cut off by conventional means, in such a way that the total length of the portion is 0.525, comprising a length 1B of 0.390" of the pure copper wire, the remainder 2B of the cut length being of the pure silver wire. (See FIGURE 3.) The composite slug of metal so produced is then transferred to a mechanical press, and, using suitable tools, is deformed at room temperature to the rivet-like form illustrated in FIGURE 4. The contact rivet produced has a silver-faced copper head 1C (the silver face being denoted by 2C) and has a copper shank 1D. The head diameter is 0.375, the head thickness is 0.062", the shank diameter is 0.156" and the shank length is 0.150".

It will be readily understood that the method described above with reference to the drawing, is not limited to the use of pure copper and pure silver only, and may be applied to other base metals and to other precious or noble metals and their alloys, which are capable of being joined together and of being deformed. The method may also be applied to metals which may not be deformed easily at room temperature, by carrying out the forming operation at elevated temperatures. Moreover, the method may be used for the manufacture of electrical contacts having a wide range of sizes and shapes, and including, for example, contacts in the form of rivets having hollow shanks.

It is possible for the head of the rivet to be formed by upsetting a slug of smaller cross-section than the crosssection of the head to be formed, or the rivet may be formed by the extrusion by conventional means of the shank from a slug of larger cross-section than that of the shank to be formed.

What we claim is:

1. The method of manufacturing a bimetallic electrical contact, comprising aligning first and second metal wires in end-to-end abutting relationship, welding the wires at the abutment thereof to form a welded joint while maintaining the abutment pressure conditions insuificient to cause upsetting and swelling at the joint, cutting off a length of wire including the joint to obtain a composite wire slug, deforming a portion of the slug including the first and second wires into the form of a rivet head and the remainder in the form of a shank integral with the head.

2. The method according to claim 1, wherein the slug first wire is composed of a noble metal and the slug second wire is composed of base metal, and deforming the References Cited by the Examiner UNITED STATES PATENTS 7/19 Hosford 29-15555 7/23 Trivelloni 29-15555 X 8/32 Siegmund 200-166 8/56 Gwyn 29 1s5.55 10 Gwyn 200-166 Josef-Johann Gutbrod et a1.

29-15555 Witt et a1. 200-166 X Graves 200-166 Zysk et a1. 200-166 WHITMORE A. WILT Z, Primary Examiner.

MAX L. LEVY, JOHN F. CAMPBELL, Examiners. 

1. THE METHOD OF MANUFACTURING A BIMETALLIC ELECTRICAL CONTACT, COMPRISING ALIGNING FIRST AND SECOND METAL WIRES IN END-TO-END ABUTTING RELATIONSHIP, WELDING THE WIRES AT THE ABUTMENT THEREOF TO FORM A WELDED JOINT WHILE MAINTAINING THE ABUTMENT PRESSURE CONDITIONS INSUFFICIENT TO CAUSE UPSETTING AND SWELLING AT THE JOINT, CUTTING OFF A LENGTH OF WIRE INCLUDING THE JOINT TO OBTAIN A COMPOSITE WIRE SLUG, DEFORMING A PORTION OF THE SLUG INCLUDING THE FIRST AND SECOND WIRES INTO THE FORM OF A RIVET HEAD AND THE REMAINDER IN THE FORM OF A SHANK INTEGRAL WITH THE HEAD. 